It’s not that older TVs won’t be able to get a clear signal. It’s that the signal is completely changing and older TVs don’t know how to process it. However, those older TVs will not become obsolete.
If you get your programming over the air: You will be able buy a converter box for about $50 that will attach to your older TV. Your regular old antenna will then be attached to this box. You will then use the converter box to change channels on your TV. It won’t be HD, but it will allow you to watch all the over the air TV channels you got before, along with any new new sub-channels your local networks have.
If you get your programming from cable or satellite: If you use a box from the cable/satellite company to tune channels you should have no changes to your viewing habits as the cable or satellite company already process all the channels for you. Otherwise you might be required to get a cable box.
Older TVs will continue to work with any equipment you currently have such as video games, DVD players, VCRs, etc.
The easiest way to determine if your TV is digital ready or not if you don’t really know what you’re looking for is to look at your TVs remote control. Along with the numbers 0–9 is there a button for a dash or a decimal? If so you probably have a digital TV as digital sub-channels are usually entered as “12–1” or “12.1” for example. If there is no dash or a decimal you probably do not have a digital TV.